I have just done some sums. I have worked out that if I undertook a journey of 160 miles with tyres worn to the 2mm mark and then swapped the tyres for new ones and did the same journey at the same speed, I would get there 3 miles sooner as it were. Getting 'free miles' sounds good to me - faster journey times are always good.

But can this be true - or am I missing something from my equation?

Work out circumference of a worn tyre and a new one, work out difference in distance travelled on one rotation of each tyre. Note the difference and after working out how many tyre rotations are needed for the worn tyre on my journey, knock off the difference between new and old.

3 less miles I make it!

TH

in theory yes... on a wet road could be more cos of the higher wheel spin

It would be only on your odometer though, the car will have worked the same (petrol useage etc).

Having a quiet day then ??????????

Try getting out a bit more :rofl:.

The distance is still 160 miles you cant change that.

Your speedo will read 157 miles

Work out circumference of a worn tyre and a new one, work out difference in distance travelled on one rotation of each tyre. Note the difference and after working out how many tyre rotations are needed for the worn tyre on my journey, knock off the difference between new and old.

TH

As others have said, the distance travelled is the same, but there will be fewer rotations of the wheel and therefore a smaller odometer reading (and lower speedometer reading too).

But are your calculations right? Did you use the nominal radius of the tyre, or the actual rolling radius allowing for the flat bit on the road? The new tyre - old tyre difference will be a bigger proportion of the rolling radius than of the nominal radius, so the actual difference would be greater than the 3% you calculated.

Gets tricky doesn't it?

Hmm. I was using a constant radius as even if the tyre is pushed flatter in one spot, the amount of tread distance covered by one wheel rotation should be a constant. But my workings could be flakey:O - that's why I put it up for debate.

TH

are you allowing for wear of the new tyre ?

It will effect the fuel, a new tyre takes a longer stride than an old one, this is why the cops allow 10% for speeding.